Download Considerations regarding the role of 99m Tc

Lidia Ionescu, Cipriana Stefanescu,
Carmen Vulpoi, C. Diaconu, Cr. Dragomir
CT –mainstay of thymic investigation
 Thoracic CT scan has a reliable sensitivity and
specificity in detecting thymic lesions
 Elective method of diagnosis
 One major difficulty is to differentiate for certain
between thymic lymphoid hyperplasia and thymoma.
 But in equivocal cases, other investigations can add
suplimentary informations.
MV, male, 46 years old, 6w. history of MG- Oss. III,
CT suspicious for thymoma,
Op. 2004, pathology- thymic lymphoid hyperplasia +
mediastinal ectopies, post. op.- complete remission
GE, 19 years old man
Hashimoto’s thyroiditis - apr. 2005- L-thyroxine,
Hemolytic anemia – oct .2005 (Hb-3,8g/dl, LDH-1444 u/l)Treatment- steroizi, transfuzii repetate.
CT- thymoma, op.dec 2005
Pathology- thymic lymphoid hypertrophy,
Result- complete remission of hemolytic anemia
PF, female, 21 years old, MG- OSS III,
CT- thymic hyperplasia, op. 1997
Pathology - lymphocitic thymoma
Result - farmacologic remission
Imaging investigations
 Equivocal cases - thymic scintigraphy can add
supplimentary informations to CT aspects.
 Equivocal cases:
 Association of thyro-thymic lesions
 Tumor recurrence
 Type of thymic lesions
 Ectopic thymomas
Scintigraphy with 99mTc-tetrofosmin
 Frequently used in the assessment of myocardial
perfusion, conducted to incidental extracardiac uptake
and detection of a mediastinal mass as it showed in few
reported cases in the literature (Kotsalou I, Hawkins M)
 This investigation is not yet included in the algorithm of
diagnosis for mediastinal mass
 But it must be considered a valuable alternative when
conventional investigations fail to confirm a clinical
suspicion, resulting in adequate decision making.
Thymic scintigraphy
 Pathological uptake of 99mTc tetrofosmin appears in
benign and malignant tumors through an incomplete
understood mechanism.
 But the increased number of mitochodrias and the
degree of perfusion of the lesion seem to play an
important role.
Thymic scintigraphy
 Thymic scintigraphy can asses after the degree of up-
take of the radiotracer on the early and late images
 Normal thymus,
 Hyperplasia
 Thymoma
 Tumor recurrence
 Ectopic thymomas
The 99m-Tc Tetrofosmin scintigraphy
 Performed with standard doses, according to the
worldwide accepted protocol.
 An informed consent for the investigation is obtained
from all the patients.
 An AXIS Gamma camera (Philips), Siemens doublehead detection and SPECT was used and acquired data
were analyzed with an IBM specialized software.
99m Tc Tetrofosmin
 Lipophile molecule that crosses the cellular
membranes according to electrochemical gradient and
fluidity of the membrane.
 It accumulates mainly in the mitochondria, which
explains the fixation in cells with intense metabolism.
Equivocal cases
 The association hyperthyroidy-myasthenia gravis is
present mainly in autoimmune thyropathies such as
Hashimoto’s thyroiditis or Grave’s disease
 Usually myasthenia gravis is secondary to
hyperthyroidy due to thymus hyperplasia and an
adequate antithyroid drug treatment or surgery result
in remission of thymic hyperplasia.
Associated lesions
Grave’s disease-myasthenia gravis
 Murakami, Yasuhiro Hosoi demonstrated the presence
of thymic hyperplasia in Grave’s disease patients,
calculating on CT scan images the size and density of
the thymus on untreated and treated Grave’s disease
patients.
 The conclusion was that thymic hyperplasia regresses
in treated patients either with antithyroid drugs or
total thyroidectomy
Thyro-thymic lesions
 Yamanaka K, Nakayama H. reported a case of Grave's
disease associated with a mediastinl mass in whom CT
scan RMI were suggestive for a thymoma.
 The patient underwent total thyroidectomy and
thymectomy at the same stage.
 Pathology report showed a thymic hyperplasia.
AM, 46-year-old woman, 2007 multinodular goitre and
myasthenia gravis
Thyroid profile (TSH-0.1 µUI/ml, fT4-1.2ng/dl),
Thyroid total volume of 65.9 ml. (Prof. dr. C. Vulpoi)
Compressive goiter
Retrosternal goiter
Total thyroidectomy for MNG-2007,
Myasthenia gravis aggravated
Normal Chest
Normal thymus
Thymic scintigraphy
Hypercaptation of 99mTc-tf. consistent with a thymoma
Repeat CT scan
Antero- inferior mediastinal mass
Thymectomy, 6 months following TT, june 2008
Paramedian low retrosternal
mass
Well-encapsulated mass
Hyperthyroidism+ectopic thymoma
 The thyroid lesion more obvious, was first treated and
myasthenia gravis considered wrongly to be secondary
and remitting after total thyroidectomy.
 On thymic scintigraphy was evident the high uptake of
Tc-TF in lower anterior mediastinum with a high
suspicion of thymoma.
 Pathology report of the specimen was mixt thymoma
with capsular microscopic invasion-Masaoka II stage.
Equivocal case
Tumour recurrence or
postoperative mediastinal scar in
patients with recurrent myasthenia
gravis??
CT, 64 years old, thymoma+MG, Oss.IV, op. 2002,
Lymphocitic thymoma (type I malignant thymoma)-Masaoka II
( well encapsulated but microscopic capsular invasion),
adhesions to left M. pleura which was resected
Radiotherapy 44 Gy, chemotherapy, 1 year CP+PDN
Pericarditis at 1 year postRxT
Remission of MG 5 years, 2008- AChE
CT aspects-2009
Retrosternal postoperative scar tissue,
pericarditis
2009
Inflammatory pericarditis
2009- POSTOPERATIVE THYMIC SCINTIGRAPHY
LACK OF RADIOTRACER UPTAKE IN THE ANTERIOR
MEDIASTINUM
Conclusion
 The thymic 99mTc tetrofosmin scintigraphy can be efficient
in diagnosing and therapeutic decision making when
conventional imaging investigations fail to confirm a
clinical suspicion.